The management and tracking of personnel, assets, and other objects is required in a wide variety of environments and is often cumbersome, labor intensive, and expensive. Radio receivers and transmitters have been used for many years to identify personnel and objects in such environments. For example, many systems are known for attaching radio tags to items, such as personnel, assets, and automobiles. When automobiles equipped with radio tags enter a certain area, such as a toll booth area, the automobiles are automatically identified. The appropriate tolls are deducted from corresponding accounts, thereby eliminating the need for drivers to stop and make payments at toll booths. When radio tags are place on personnel, they can be automatically identified and checked for authorized entry to a facility in a security application called access control. Assets which are tagged can be identified and tracked as they move throughout a facility for the purposes of automatically locating them. They can also be automatically counted therefore providing inventory control. They can also be protected as when an asset approaches an exit doorway the system can automatically determine if the asset is authorized to be removed from the facility. Tagged vehicles, assets, and personnel can be linked logically in the system to enable greater visibility and control.
RFID systems generally use a fixed position transmitter capable of reading remote, portable tags attached to personnel, assets, or other objects. Because of power consumption concerns and the life span of the tag, the radio tag often operates only after receiving a wake-up signal, often called semi-active operation. The wake-up signal is generated by a powered device called an activator which transmits the desired signal through a specially designed antenna based upon the physical properties of the area. Activation causes the tag to leave a low power, or sleep state and enter an active state. The activation transmitter produces the wake-up signal, and an antenna transmits the wake-up signal to a particular area.
Although semi-active radio tags are common, many applications alternatively use passive radio tags. Passive tags are tags that do not contain a battery. Instead, power for the tag is supplied by the tag reader (radio waves from the reader cause a magnetic field to be formed around the antenna of the tag, and the field is used to energize the circuits in the tag). One particular application of passive radio tags is in association with the EPCglobal standard. The EPC standard pairs the use of RFID systems with electronic product codes (EPCs) for management of high volume consumer package goods. This standard is effective at automatically identifying pallets, cartons, and individual items as they enter a warehouse facility via an entry/exit door portal. The current standard is limited in its use and reliability because the passive RFID system solution requires substantial tag activation electronics to be located proximate to the tagged goods in order for the tag to have enough reflective energy for the signal to be read and in order for the system to be reliable. Furthermore, careful orientation of tag to reader is a paramount concern in order to achieve reasonable performance. The result is a limited tag-to-reader range.